Search Results (5 total)

Angular distributions for the elastic scattering of ⁸Li on ⁹Be and the neutron transfer reactions ⁹Be(⁸Li,⁷Li)¹⁰Be and ⁹Be(⁸Li,⁹Li)⁸Be were measured with a 27 MeV ⁸Li radioactive nuclear beam. Spectr- oscopic factors for ⁸Li ⊗n= ⁹Li and ⁷Li ⊗n= ⁸Li bound systems were obtained from the comparison between the experimental differential cross section and finite-range distorted-wave Born approximation calculations with the code FRESCO. The spectroscopic factors obtained were compared to shell model calculations and to other experimental values from (d,p) reactions. Using the present values for the spectroscopic factor, cross sections for the direct neutron-capture reactions ⁷Li(n,γ)⁸Li and ⁸Li(n,γ)⁹Li were calculated in the framework of a potential model.

Fusion excitation functions are measured for the α,p, and n evaporation channels in the fusion of the ¹²C+¹²C system at center-of-mass energies between 4.42 and 6.48 MeV, with energy steps of 75 keV. The γ-ray technique is used with a new absolute normalization method which is independent of charge collection, allowing one to monitor at the same time the carbon buildup at the target. Discrepancies between previous works are discussed and a simple unification is proposed. Barrier penetration model (BPM) calculations are consistent with a belly-to-belly orientation of the oblate deformed ¹²C nuclei at the touching point. As in previous works, much structure is seen in the excitation function which is nearly consistent with the positions of resonances reported in the literature for this system. Using BPM predictions for the background excitation function and doing a simultaneous fit of the relevant Breit-Wigner terms in the measured energy region produced a modified set of resonance parameters. The extrapolation of the astrophysical S factor to lower energies is discussed on the basis of the unified data.

The cross section for α-particle emission in the ⁶He+²⁰⁹Bi reaction at energies near the Coulomb barrier is remarkably large. Possible reactions that may produce the observed α particles include two-neutron transfer, one-neutron transfer, and direct projectile breakup. Each of these mechanisms results in a distinctive angular correlation between the α particle and the outgoing neutron(s). A neutron-α-particle coincidence experiment was performed to study two-neutron transfer to unbound states of ²¹¹Bi. It is shown that approximately 55% of the observed α-particle yield at and beyond the grazing angle is because of this process. This is more than 2.5 times the fraction attributable to single-neutron transfer. The corresponding 2n-transfer cross section is 0.4 ± 0.1 b.

The interaction of ⁶He with ²⁰⁹Bi has been studied over a range of energies well below the nominal Coulomb barrier. A ⁴He group of remarkable intensity, first observed in a previous experiment at near-barrier energies, continues to dominate the reaction in the sub-barrier regime. A total cross section of nearly 200 mb was measured for this group at 6 MeV below the barrier. This very large value is shown to be consistent with the total reaction cross section deduced from a simultaneously-measured elastic scattering angular distribution.

Reaction products from the interaction of ⁶He with ²⁰⁹Bi have been measured at energies near the Coulomb barrier. A ⁴He group of remarkable intensity, which dominates the total reaction cross section, has been observed. The angular distribution of the group suggests that it results primarily from a direct nuclear process. It is likely that this transfer and/or breakup channel is the doorway state that accounts for the previously observed large sub-barrier fusion enhancement in this system.